1. Field of the Invention
The present invention relates to a data transmission processing system in which audio data and video data or one of the same (hereinafter referred to as "audio and/or video data") and time code data are multiplexed in a same transmission packet and transmitted and received among a plurality of communication nodes connected via a communication network (communication line) of an asynchronous transfer mode (ATM) etc.
2. Description of the Related Art
There are cases where time code data indicating a connecting point (IN point, OUT point, editing point) etc. of the audio and/or video are added to the audio and/or video data (source data) per se so as to facilitate the editing etc. An editing apparatus monitors the time code data of the audio and/or video data generated (reproduced) by a video tape recorder (VTR) apparatus and controls the VTR apparatus according to the editing points (time code data) of the audio and/or video data designated by the editor to make the VTR apparatus reproduce and record the audio and/or video data.
Further, recently, an asynchronous transfer mode (ATM) system has been put into practical use as a high speed digital data transmission system. Application to the transmission of audio and/or video data by the ATM system is being studied.
Therefore, there is a demand for connecting an editing apparatus and a VTR apparatus via a communication network such as an ATM communication network and controlling the VTR apparatus from the editing apparatus via the communication network so as thereby to edit the audio and/or video data. In order to perform such remote editing, the editing apparatus must transmit the control data for the VTR apparatus to the VTR apparatus via the communication network, and the VTR apparatus must reproduce the audio and/or video data according to the sent control data. Further, the reproduced audio and/or video data and time code data must be transmitted to the editing apparatus again via the communication network, and the editing apparatus must perform the editing based on the received audio and/or video data and time code data and record the same.
However, a transmission delay is produced while the data is transmitted to the opposite side via the communication network. For example, there is a possibility that the transmission delay will change along with the elapse of time due to the state of congestion etc. of the communication network in the ATM communication network and therefore when the time code data and the audio and/or video data are separately transmitted, a "time lag" will sometimes be produced between the time code data and the audio and/or video data received by the editing apparatus. When a time lag is produced between the time code data and the audio and/or video data in this way, the audio and/or video data cannot be connected at the correct timing and correct editing will become difficult.
On the other hand, time code data referred to as a "virtual interval time code (VITC)" is inserted in the vertical retrace line period of the audio and/or video data as part of the source data, so it may also be considered to use the VITC for the remote editing. This VITC has a characteristic feature that the audio and/or video data can be read also at the time of "still reproduction" when the audio and/or video data is being reproduced by the VTR apparatus in a freeze state.
However, where the audio and/or video data do not contain a VITC or contain an erroneous VITC, if the remote editing is carried out with respect to such audio and/or video data, only incorrect editing can be carried out.